About this Research Topic

Background

Self-fertilization, where pollen from a plant pollinates the flowers of the same plant and sets seeds, is the extreme case of inbreeding that involves mating among close relatives. One genetic consequence of selfing is the reduction in the level of heterozygosity in the progeny – a drastic reduction of 50% heterozygosity in just one generation of selfing for diploid species, and in 3.8 generations of an autotetraploid species. As a result, deleterious effects of genetic load are likely to be expressed following inbreeding and lead to negative impact on yield and plant fitness, a phenomenon referred to as inbreeding depression (ID). Inbred plants may show less resistance to herbivores relative to outcrossed plants, succumb to more damage by herbivores and produce fewer defense compounds facilitating their reproduction.

The partial recessive model for inbreeding depression assumes that most of the genetic load consists of predominantly recessive or partial recessive deleterious alleles. These alleles are expressed when they become homozygous following inbreeding, and, hence, create ID. The expression pattern of inbreeding depression can vary across fitness traits, life history stages, and among species. Inbreeding depression is higher in outcrossing relative to selfing species, on average, supporting the prediction that continuous selfing reduces ID. The highest level of ID tends to occur in the seed maturation stage in outcrossing species, and in the later growth-and-reproduction stage for selfing species. Such differences in ID among selfers and outcrossers suggest that early-acting ID may result from large-effect recessive alleles that can be purged while late-acting ID is more difficult to purge and may be due to many mildly deleterious recessive alleles.

Level of inbreeding depression and selfing rates are closely connected. Selfing increases homozygosity which, in turn, results in the expression of ID. Conversely, ID is a key determining parameter that can influence the subsequent evolution of selfing and the mating system. Other factors, such as population size, the inbreeding coefficient and the ploidy level, can also influence the magnitude of inbreeding depression. One expects lower inbreeding depression in small, highly inbred populations where the recessive genes with large effects may have been purged over time. Higher ploidy levels, often seen in crop plants, are expected to slow down the expression of ID resulting from the expression of deleterious alleles. However, studies on ID of autotetraploid wild plant species and crops, often reveal a substantially higher than expected level of ID, approaching the level found in diploid species. Such findings challenge both theoretical and practical understanding of ID. Factors such as the rapid loss of multiple-allelic interactions within a locus, the level of dominance, and diploidization of sections of the genome have been suggested as potential factors increasing the level of ID in autotetraploids. Connecting studies of ID in polyploid plants in natural populations and crop systems could increase our understanding of the factors affecting ID in plants.

This Research Topic aims to provide novel insights into how mating system and inbreeding depression shape plant populations and affect crop yield. Inbreeding depression influences the evolution of plant mating systems, and the mating system and inbreeding depression can impact the persistence of plant populations, range expansion, pollinator attraction, plant fitness, and the potential for adaptation to changing environments. In agriculture, inbreeding depression can affect the development of hybrids and impact crop yield. Research is also needed to better elucidate the factors behind the higher than expected level of ID in polyploid plants. These questions can be examined across multiple scales, from a theoretical or empirical perspective, emphasizing a genetics or ecological angle, at the population level or using a phylogenetic approach. This special issue aims to introduce new perspectives derived from these diverse approaches on the many ways mating system and inbreeding depression shapes plant populations and influence agricultural systems. For this article collection, original research articles, reviews and perspectives will be considered. The following non-exhaustive themes will be considered for the contributions:

- The impact of pollinators on plant mating system and inbreeding depression

- The influence of inbreeding depression on crop yield

- The impact of plant mating system and inbreeding depression on range expansion

- Management practices that affect selfing and inbreeding depression in agricultural systems

- Relationship between ploidy and inbreeding depression, and its impact on plant fitness

- Factors that slow down purging in natural populations and agricultural systems

- Mechanisms responsible for the greater than expected level of ID in polyploid plants

- Inbreeding, inbreeding depression and demography of plant populations

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.

Keywords: changing environment, crop yield, inbreeding, inbreeding depression, outcrossing, plant reproduction, pollinator attraction, purging of alleles, selfing, range expansion

Important note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.

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